In Summary:
You must be online for at least 3 hours to get a reward. 3 hours AFK'ing won't work. You must earn EXP / do kills / play. You don't have to play actively for full 3 hours, but you must be online for at least 3 hours and play actively at least some of that time.
Rewards are not sent out instantly. Rewards are sent out every day at 00:00 CET and 03:01 CET.
If you did not get a reward, you either weren't online long enough (at least 3 hours) or you didn't get enough kills / exp / played enough (we use multiple methods to find out if you actually played).